question_answer

    An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength   so   emitted   illuminates   a photo-sensitive material having work function 2.75 eV. If the stopping potential of the photo-electron is 10 V, the value of n is

A)  3                            

B)  4                            

C)  5                            

D)  2

Correct Answer: A

Solution :

\[E=K{{E}_{\max }}+W\] \[=e{{V}_{0}}+W\] \[=10+2.75\] \[E=12.75\,eV\] Difference of 4 and 1 energy level is 12.75 eV. So, higher energy level is 4 to ground and excited state is n = 3.